Astrophysics

GRE Subject Test: Physics · Learn by Concept

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GRE Subject Test: Physics › Astrophysics

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1

If the temperature of a blackbody doubles, what occurs to the wavelength of maximum emission?

It is halved.

CORRECT

It doubles.

0

It quadruples.

0

No change.

0

It is quartered.

0

Explanation

This is an application of Wein's Law that states the following:

, where is the wavelength of maximum emission of the object (measured in ), and is the temperature in . Since the wavelength and the temperature are inversely proportional, if we double the temperature, we must cut the wavelength by the same proportion. Therefore, the temperature must be halved.

2

By what factor will the energy emitted each second off the surface of a blackbody change if the the temperature of the object is tripled?

CORRECT

0

0

0

0

Explanation

Stefan-Boltzmann's equation for a blackbody states:

, where is the energy emitted each second, is the Stefan-Boltzmann constant, and is the temperature of the blackbody. Therefore, if we triple the temperature, the energy will increase by a factor of

3

Using the kinetic theory of gas, what is the fundamental property of a planet that dictates if it is able to retain an atmosphere?

Mass

CORRECT

Temperature

0

Energy

0

Number of moons

0

Magnetic field strength

0

Explanation

The kinetic theory of gas states:

. Whenever the velocity of the individual gas particles is larger than the escape speed of the planet,

, the gas particles will leak into space and deplete the atmosphere. The physical property that determines this is the mass of the planet.